Take this scenario

Consider the following model that is used to collect User rating on a web item.

class Rating
include Mongoid::Document

field :comment, :type => String
field :value, :type => Integer
field :email, :type => String
field :other
field :data

scope :rated_a, lambda

{|val| where(:value => val) }

end

Now if you try to access the scope, after you specify only() criteria, you are no longer able to use a scope with an argument.

Rating.only(:_id, :value, :comment, :email).where(:email => 'joe@somewhere.com').rated_a(5)

This will return with:

ArgumentError: wrong number of arguments (1 for 0)

But this works:

Rating.where(:email => 'joe@somewhere.com').rated_a(5)

As well as this:

Rating.where(:email => 'joe@somewhere.com').rated_a(5).only(:_id, :value, :comment, :email)